In conventional resin sealing molding, transfer molding or injection molding has been used. In transfer molding or injection molding, a resin flow channel and a cavity each provided to a die for resin molding are used. A fluid resin is introduced into the cavity through the resin flow channel. The introduced fluid resin is set to form a set resin. Thereby, a molded object having the set resin is completed. For example, thermosetting resin such as epoxy resin or the like is used as the fluid resin, and a steel material such as tool steel, a cemented carbide (a WC—Co type alloy), or the like is used as a material for the die. It is preferable in this case to reduce adhesion property between the set resin and the surface of the die (die surface), in other words, to improve releasability between the set resin and the die surface, for easy removal of the molded object.
The inventors of the present application have found that Y2O3 (yttria), which is a sintered body stable in the air, has a low-adhesion property with respect to epoxy resin. The term “low adhesion property” described herein refers to “having a low adhesion property when comparison is made in terms of adhesion property between a conventional material for a die such as a steel material, a cemented carbide, or the like and a basic substance represented by epoxy resin”. The inventors of the present application have proposed to use an oxide such as Y2O3 (a basic oxide) to form a die surface or a resin molding die (see Japanese Patent Laying-Open No. 2005-274478, pages 8 to 9 and FIG. 2).
In another patent application filed by the applicants of the present application, a Y2O3 solid solution, an yttria composite oxide (LaYO3), and a mixture of a Y2O3 solid solution and an yttria composite oxide are described as low adhesion materials forming a resin molding die (Japanese Patent Application No. 2006-017335). According to these techniques, a basic oxide such as Y2O3, a Y2O3 solid solution, or the like, which is a material less adhesive to a set resin, is contained in a material for a resin molding die forming a die surface. Thereby, a resin molding die excellent in releasability is implemented. It is to be noted that the invention disclosed in Japanese Patent Application No. 2006-017335 has not been published yet.
However, according to the conventional techniques described above, that is, the techniques of using a material for a resin molding die containing a basic oxide such as Y2O3, a Y2O3 solid solution, or the like (hereinafter referred to as a “basic oxide or the like”) to form a die surface or a resin molding die, there are two problems as described below.
The first problem is that the resin molding die has insufficient wear resistance. This can be highly problematic especially when a chip-type electronic component (hereinafter referred to as a “chip”) such as an LSI (Large Scale Integration) chip mounted on a lead frame, a printed board (hereinafter referred to as a “board”), or the like is sealed with resin. In this case, thermosetting resin (for example, epoxy resin) containing a ceramic filler is used as a fluid resin. The basic oxide or the like forming the die surface of the resin molding die is worn by the filler.
The second problem is that the basic oxide or the like is likely to have chipping when impact is applied from outside, in other words, it has low impact resistance. Therefore, although it is possible to obtain a resin molding die excellent in releasability according to the techniques of using a basic oxide or the like, which is merely a low adhesion material, to form a die surface or a resin molding die, it has been difficult to obtain a resin molding die having both excellent wear resistance and impact resistance. Patent Document 1: Japanese Patent Laying-Open No. 2005-274478 (pages 8 to 9, FIG. 2)